The objective of the present study was to examine the effect of dietary protein intake on hormone levels and the hormonal response to stress. Male, Fischer 344 rats were fed diets containing 4, 8, 12, 24, or 48% protein for a 15 month period. Plasma levels of corticosterone (CS), aldosterone, testerone, triiodothyronine (T3), thyroxine (T4), thyrotrophic stimulating hormone (TSH), total protein, and albumin were determined at several ages in non-stressed rats and in rats stressed by immobilization. Hormone levels of non-stressed rats were not influenced by dietary protein intake. Stress resulted in significantly increased levels of corticosterone and aldosterone while T3, T4, and TSH were not elevated as a result of immobilization. Corticosterone and aldosterone levels were elevated in immobilized rats fed the 48% protein diets in comparison to the 134, 8, 12, and 24% groups. By 3 hours following immobilization, CS and aldosterone levels in the 48% group were similar to prestress levels and similar to the other dietary groups. The apparent hyper-responsiveness of the adrenal of high protein fed rats may be a result of the increased need for conversion of protein to glucose in rats fed high protein, low carbohydrate diets.